The present invention relates to a method of manufacturing a semiconductor device, and can be suitably used, for example, in a method of manufacturing a semiconductor device having a nonvolatile memory.
EEPROM (Electrically Erasable and Programmable Read Only Memory) is widely used as a nonvolatile semiconductor memory device capable of electrically writing and erasing. These storage devices typified by flash memory which are widely used at present have a conductive floating gate electrode or a charge trapping dielectric film surrounded by an oxide film below a gate electrode of a MISFET, and the charge storage states of the floating gate or the charge trapping dielectric film are used as storage information, and the storage information is read out as thresholds of transistors. The charge trapping dielectric film is a dielectric film capable of storing charges, and an example thereof is a silicon nitride film or the like. By injecting and discharging charges into and from the charge storage region, the threshold of MISFET (Metal Insulator Semiconductor Field Effect Transistor) is shifted to operate as a storage device. When a charge trapping dielectric film such as a silicon nitride film is used as the charge storage region, it has advantages such as thinning of the oxide films located above and below the silicon nitride film because it is excellent in reliability of data retention because charges are stored discretely, and lowering of the voltage of writing and erasing operations, as compared with the case where a conductive floating gate film is used as the charge storage region.
Japanese unexamined Patent Application Publication No. 2008-538868 describes a manufacturing method of a flash memory using a self-aligned STI structure (SASTI). For example, if the etching process of the ONO layer is performed after the STI structure is formed, an ONO residue is generated on the side surface of the STI structure, and the product yield is lowered. Therefore, a manufacturing method of forming an STI structure by patterning an STI trench after forming an ONO layer is disclosed.